The weak matrix in concrete, when reinforced with steel fibres, uniformly distributed

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FIBER REINFORCED CONCRETE- BEHAVIOUR PROPERTIES AND
APPLICATION

Dr. M. C. Nataraja

Professor of Civil Engineering,
Sri Jayachamarajendra College of engineering, Mysore-570 006
(nataraja96@yahoo.com)

Introduction
The weak matrix in concrete, when reinforced with steel fibres, uniformly distributed
across its entire mass, gets strengthened enormously, thereby rendering the matrix to
behave as a composite material with properties significantly different from
conventional concrete. Because of the vast improvements achieved by the addition of
fibers to concrete, there are several applications where Fibers Reinforced Concrete
(FRC) can be intelligently and beneficially used. These fibers have already been used
in many large projects involving the construction of industrial floors, pavements,
highway-overlays, etc. in India. The principal fibers in common commercial use for
Civil Engineering applications include steel (SFRC/SFRS), glass, carbon and aramid.
These fibers are also used in the production of continuous fibers and are used as a
replacement to reinforcing steel. High percentages of steel fibers are used extensively
in pavements and in tunnelling. This invention uses Slurry Infiltrated Fiber Concrete
(SIFCON). Fibers in the form of mat are also being used in the development of high
performance structural composite. Continuous fiber-mat high performance fiber
reinforced concrete (HPFRCs) called Slurry Infiltrated Mat Concrete (SIMCON) is
used in the production of High performance concrete. Use of basalt fibers are picking
up in western countries. Steel fibers are also used in the production new generation
concretes such as Reactive Powder Concrete (RPC), Ductal and Compact Reinforcing
Concrete (CRC). Properties and applications of SFRC and some of these new
generation fiber concrete materials are discussed.

1. Steel Fibre Reinforced Concrete (SFRC)
Concrete is the most widely used structural material in the world with an annual
production of over seven billion tons. For a variety of reasons, much of this concrete is
cracked. The reason for concrete to suffer cracking may be attributed to structural,

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environmental or economic factors, but most of the cracks are formed due to the inherent
weakness of the material to resist tensile forces. Again, concrete shrinks and will again
crack, when it is restrained. It is now well established that steel fibre reinforcement offers
a solution to the problem of cracking by making concrete tougher and more ductile. It has
also been proved by extensive research and field trials carried out over the past three
decades, that addition of steel fibres to conventional plain or reinforced and prestressed
concrete members at the time of mixing/production imparts improvements to several
properties of concrete, particularly those related to strength, performance and durability.

The weak matrix in concrete, when reinforced with steel fibres, uniformly distributed
across its entire mass, gets strengthened enormously, thereby rendering the matrix to
behave as a composite material with properties significantly different from conventional
concrete.

The randomly-oriented steel fibres assist in controlling the propagation of micro-cracks
present in the matrix, first by improving the overall cracking resistance of matrix itself,
and later by bridging across even smaller cracks formed after the application of load on
the member, thereby preventing their widening into major cracks (Fig. 1).

Fig. 1 Failure mechanism and the effect of fibers

The idea that concrete can be strengthened by fibre inclusion was first put forward by
Porter in 1910, but little progress was made in its development till 1963, when Roumaldi
and Batson carried out extensive laboratory investigations and published their classical

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paper on the subject. Since then, there has been a great wave of interest in and
applications of SFRC in many parts of the world. While steel fibres improve the
compressive strength of concrete only marginally by about 10 to 30%, significant
improvement is achieved in several other properties of concrete as listed in Table. Some
popular shapes of fibres are given in Fig.2.

Fig. 2 Different types of steel fibers
In general, SFRC is very ductile and particularly well suited for structures which are
equired to exhibit:
• Resistance to impact, blast and shock loads and high fatigue
• Shrinkage control of concrete (fissuration)
• Very high flexural, shear and tensile strength
• Resistance to splitting/spalling, erosion and abrasion
• High thermal/ temperature resistance
• Resistance to seismic hazards.
The degree of improvement gained in any specific property exhibited by SFRC is
dependent on a number of factors that include:
• Concrete mix and its age
• Steel fibre content
• Fibre shape, its aspect ratio (length to diameter ratio) and bond characteristics.

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The efficiency of steel fibres as concrete macro-reinforcement is in proportion to
increasing fibre content, fibre strength, aspect ratio and bonding efficiency of the fibres in
the concrete matrix. The efficiency is further improved by deforming the fibres and by
resorting to advanced production techniques. Any improvement in the mechanical bond
ensures that the failure of a SFRC specimen is due mainly to fibres reaching their ultimate
strength, and not due to their pull-out.

1.1 Mix Design for SFRC
Just as different types of fibres have different characteristics, concrete made with steel
fibres will also have different properties.
When developing an SFRC mix design, the fibre type and the application of the concrete
must be considered. There must be sufficient quantity of mortar fraction in the concrete to
adhere to the fibres and allow them to flow without tangling together, a phenomenon
called ‘balling of fibres’. Cement content is, therefore, usually higher for SFRC than
conventional mixes Aggregate shape and content is critical. Coarse aggregates of sizes
ranging from 10 mm to 20 mm are commonly used with SFRC. Larger aggregate sizes
usually require less volume of fibres per cubic meter. SFRC with 10 mm maximum size
aggregates typically uses 50 to 75 kg of fibres per cubic meter, while the one with 20 mm
size uses 40 to 60 kg. It has been demonstrated that the coarse aggregate shape has a
significant effect on workability and material properties. Crushed coarse aggregates result
in higher strength and tensile strain capacity. Fine aggregates in SFRC mixes typically
constitute about 45 to 55 percent of the total aggregate content.
Typical mix proportions for SFRC will be: cement 325 to 560 kg; water-cement ratio 0.4-
0.6; ratio of fine aggregate to total aggregate 0.5-1.0; maximum aggregate size 10mm; air
content 6-9%; fibre content 0.5-2.5% by volume of concrete. An appropriate pozzolan
may be used as a replacement for a portion of the Portland cement to improve workability
further, and reduce heat of hydration and production cost.
The use of steel fibres in concrete generally reduces the slump by about 50 mm. To
overcome this and to improve workability, it is highly recommended that a super
plasticizer be included in the mix. This is especially true for SFRC used for high-
performance applications.Generally, the ACI Committee Report No. ACI 554 ‘Guide for
Specifying, Mixing, Placing and Finishing Steel Fibre Reinforced Concrete’ is followed
for the design of SFRC mixes appropriate to specific applications.


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1.2 Factors Controlling SFRC

• Aspect ratio, l/d

Volume fraction, v
f

Fiber reinforcing index, RI=l/d x v
f

Critical length, l
min
• Balling of fibers
• Good mix design: more matrix, small aggregate, workable
• Type of fibers-size, shape, strength, modulus






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1.2.1 Workability
• We know that it is usually wrong to add water to concrete for workability.
• The main problem with workability of steel fiber reinforced concrete is in getting
proper distribution of the fibers so that they don't ball up.
• This difficulty is usually overcome by slow, continuous and uniform feeding of the
fibers into the wet or dry mix by means of vibratory feeders.
• Sometimes the fibers are passed through screens as they are introduced. Proper
feeding can virtually eliminate the problem of balling. On the other hand, addition of
water to improve workability can reduce the flexural strength significantly, a critical
matter when one considers that one of the main reasons for using steel fibers is to
improve the flexural strength.
• In such cases use of suitable admixture probably would improve the workability to
certain extent and may not to the extent that you require
Test for workability
• Slump test- subsidence in mm
• Inverted slump test-time in seconds
• Compacting factor test-degree of compaction
• VB test-time in seconds. The relationship among the different workability
parameters are shown in Fig. 3. The effect of volume fraction and aspect ratio on
VB time is shown in Fig. 4

Fig.4. VB time vs percentage of fibers

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Fig.4. VB time vs percentage of fibers

Mechanical properties and strength of SFRC

The various properties of SFRC and other FRCs can be seen in the following figures.

Relative strength and toughness of the fiber reinforced mortar and concrete can be seen in
Fig. 5 As the percentage of fibers increases, the strength and toughness of fiber concrete
increases.

The increase in toughness and the effect of aspect ratio can be seen in Fig. 6. The effect of
different types of fibers on the uniaxial tensile strength is presented in Fig. 7. The
variation of compressive strength and the strain is shown in Fig. 8. The strain of SFRC
corresponding to peak compressive strength increases as the volume fraction of fibers
increases. As aspect ratio increases, the compressive strength of SFRC also increases
marginally.

The load vs deflection of SFRC beam subjected to bending is presented in Figs 9 and 10.
As the load increases, the deflection also increases. However the area under the load –
deflection curve also increases substantially depending the type and amount of fibers
added.


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Fig. 5 Relative strength vs percentage of aligned fibers


Fig. 6 Toughness and strength in relation to plain concrete

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Fig. 7 Uniaxial tensile strength vs strain for different FRCs


Fig. 8 Compressive strength vs strain diagram for SFRC
Fig. Toughness ratio definition

0
1
0

2
0

3
0

4
0

5
0

6
0

0

0.00
0.00
0.00
0.01
2
0.01
Strain,
mm/mm

Compressive strength,
Inflection point

o
A
B
C
TR = Area OABC/(f
'
cf
x 0.015)
εεεε
of

f
'
cf

10




Fig. 10 Schematic load-deflection curves for fiber composites in bending


1.3 Fibre Shotcreting
“Shotcreting” using steel fibres is being successfully employed in the construction of
domes, ground level storage tanks, tunnel linings, rock slope stabilization and repair and
4
3
2
1
L
P/2 P/2
B
A
O
C
Fig.9 Schematic load-deflection curves for fiber composites in bending
Load, P
Deflection,
δ
δδ
δ

A = First crack strength
B = Ultimate strength
I
t
=
Area OABF

Area OAKL
Area OABEG

Area OAJ
I
(ACI)old
=
E
δ
f

A
B
K
G
L J
P
F
1.9 mm
LVDT or Dial gauge
Fiber-reinforced beam
Un-reinforced matrix beam
(closed-loop testing system)
O
Total load, P
Deflection,
δ
δδ
δ


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retrofitting of deteriorated surfaces and concrete. Steel fibre reinforced shotcrete is
substantially superior in toughness index and impact strength compared to plain concrete
or mesh reinforced shotcrete.

In Scandinavian countries, shotcreting is done by the wet process and as much as 60% of
ground support structures (tanks and domes) in Norway are constructed using steel fibres.
In many countries including India, steel fibre shotcrete has been successfully used in the
construction of several railway and penstock tunnels.

1.4 Applications of SFRC
The applications of SFRC depend on the ingenuity of the designer and builder in taking
advantage of its much enhanced and superior static and dynamic tensile strength,
ductility, energy-absorbing characteristics, abrasion resistance and fatigue strength.
Growing experience and confidence by engineers, designers and contractors has led to
many new areas of use particularly in precast, cast in-situ, and shotcrete applications.
Traditional application where SFRC was initially used as pavements, has now gained
wide acceptance in the construction of a number of airport runways, heavy-duty and
container yard floors in several parts of the world due to savings in cost and superior
performance during service.
The advantages of SFRC have now been recognised and utilised in precast application
where designers are looking for thinner sections and more complex shapes. Applications
include building panels, sea-defence walls and blocks, piles, blast-resistant storage cabins,
coffins, pipes, highway kerbs, prefabricated storage tanks, composite panels and ducts.
Precast fibre reinforced concrete manhole covers and frames are being widely used in
India, Europe and USA.
Cast in-situ application includes bank vaults, bridges, nosing joints and water slides.
“Sprayed-in” ground swimming pools is a new and growing area of shotcrete application
in Australia. SFRC has become a standard building material in Scandinavia.
Applications of SFRC to bio-logical shielding in atomic reactors and also to waterfront
marine structures which have to resist deterioration at the air-water interface and impact
loadings have also been successfully made. The latter category includes jetty armor,
floating pontoons, and caissons. Easiness with which fibre concrete can be moulded to
compound curves makes it attractive for ship hull construction either alone or in
conjunction with ferrocement.

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SFRC shotcrete has recently been used for sealing the recesses at the anchorages of post
stressing cables in oil platform concrete structures. Recent developments in fibre types
and their geometry and also in concrete technology and equipment for mixing, placing
and compaction of SFRC and mechanized methods for shotcreting have placed
Scandinavian and German consultants and contractors in a front position in fibre-
shotcreting operations world wide.
Laboratory investigations have indicated that steel fibres can be used in lieu of stirrups in
RCC frames, beams, and flat slabs and also as supplementary shear reinforcement in
precast, thin-webbed beams. Steel fibre reinforcement can also be added to critical end
zones of precast prestressed concrete beams and columns and in cast-in-place concrete to
eliminate much of the secondary reinforcement. SFRC may also be an improved means of
providing ductility to blast-resistant and seismic-resistant structures especially at their
joints, owing to the ability of the fibres to resist deformation and undergo large rotations
by permitting the development of plastic hinges under over-load conditions.

1.5 General Application of Steel Fibres
1.5.1 General Applications and Advantages steel fiber concrete
Steel Fiber Reinforced Concrete or Shotcrete (SFRC/SFRS) have been used in various
applications throughout the world. In India their use is picking up slowly. The principal
advantages of SFRC versus plain or mesh/bar reinforced concretes are:

• Cost savings of 10% - 30% over conventional concrete flooring systems.
• Reinforcement throughout the section in all directions versus one plane of
reinforcement (sometimes in the sub-grade) in only two directions.
• Increased ultimate flexural strength of the concrete composite and thus thinner
sections.
• Increased flexural fatigue endurance and again thinner slabs.
• Increased flexural toughness, or the ability to absorb energy.
• Increased impact resistance and thus reduced chipping and joint spalling.
• Increased shear strength and thus the ability to transfer loads across joints in thin
sections.
• Increased tensile strength and tensile strain capacity thus allowing increased
contraction/construction joint spacing

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The six major areas in which Steel Fibers can be used to achieve hi-strength, durable
and economical concrete are:

a) Overlays
Roads, Airfields, Runways, Container, Movement and Storage Yards, Industrial Floors
and Bridges.

Advantages of using SFRC
• Fatigue and impact resistance increased
• Wear and tear resistance increased
• Joint spacing increased
• Thinner pavements possible due to higher flexural strength of SFRC
• Long service life with little or no maintenance

b) Pre-cast Concrete Products
Manhole covers and Frames, Pipes, Break-Water Units, Building Floor and Walling
Components, Acoustic Barriers, Krebs, Impact Barriers, Blast Resistant Panels, Vaults,
Coffins etc.

Advantages of using SFRC
• Fatigue and impact resistance increased
• Thinner sections possible with SFRC reducing handling and transportation costs.
• Reduced consumption and savings in cost of materials makes pre-cast products
competitive in price with cast iron or reinforced concrete products.
• Products possess increased ductility and resistance to chipping and cracking.
SFRC products suffer less damage and loss during handling and erection
• Overall improvement in all structural properties
• Many different sizes and shapes of pre-cast units possible with SFRC.

c) Hydraulic and Marine Structures
Dams, Spillways, Aprons, Boats and Barges, Sea Protection Works.


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Advantages of using SFRC
• Outperforms conventional materials by exhibiting superior resistance to
cavitations and impact damage due to wave action, hydraulic heads and
swirling water currents.
• Ideally suitable for repair of hydraulic and marine structures

d) Defence and Military Structures
Aircrafts Hangers, Missile and Weaponry Storage Structures, Blast Resistant
Structure, Ammunition Production and Storage Depots, Underground Shelters etc.

Advantages of using SFRC
• Exhibits high ductile and toughness resulting in superior resistance to blast,
impact and falling loads and missiles.
• Fragmentation effect very less compared to other material due to confinement
effect of fibers on concrete.
• Far superior resistance to fire and corrosion
• High resistance to penetration by drills hammers etc, almost impenetrable.
• A highly versatile material with longer service life.

e) Shotcreting Applications
Tunnel Linings, Domes, Mine Linings, Rock-Slope Stabilization, Repaint and
Restoration Distresses Concrete Structures etc.

Advantages of using SFRC
• Highly efficient, convenient and economical compared to mesh and bar
reinforcement used in conventional shot crating.
• One stage operation for irregular profiles.
• High resistance to abrasion and impact loads.
• Reduction in 'shadow' effects resulting in compact and dense layer.
• Improvement in ductility
• Only high performing technique suitable for tunnel and drainage lining, rock
stabilization jobs and also for repair of bridges, dams, storage tanks etc.
• Construction of energy-efficient domes and shell structures possible.

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f) Special Structures
Machine Foundations, Currency Vaults and Strong Rooms, Impact and Fiber-
Protective Shells and Lost Forms, Column-Beam Joints in Seismic-Resistant
Structures, End Zones of Prestressed Concrete Elements, High Volume Steel Fiber
Reinforce Concrete structures made out of SIFCON and CRC (Slurry Infiltrated Fiber
Concrete and Compact Reinforced Concrete)

Advantages of using SFRC
• Improved performances under action of any kind of loading
• High seismic-resistance in buildings due to ductile behaviours of joints and
connections

1.5.2 Some applications in India
Fiber reinforced concrete is in use since many years in India, but the structural
applications are very much limited. However, its application is picking up in the recent
days. Following are some of the major projects where large quantities of steel fibers are
used.

1. More than 400 tones of Shaktiman Steel Fibers have been used recently in the
construction of a road overlay for a project at Mathura (UP).
2. They have also been successfully used at the end anchorage zones of prestressed
concrete girders for resisting bursting and spalling forces in bridge projects in
Bangalore and Ahmedabad executed by one of the reputed construction
companies.
3. The fibers have also been used for heavy-duty industrial floors.
4. Other projects include Samsonity Factory-Nasik, BIPL Plant-Pune, KRCL-
MSRDC tunnels, Natha Jakri Hydro Electric Plant, Kol HEP, Baglihar HEP,
Chamera HEP, Sala HEP, Ranganadi HEP, Sirsisilam project, Tehri Dam
project, Uri Dam Project, etc.
5. Used in many tunnelling projects and for slope stabilisation in India.

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2. High-Performance Composite Infrastructural Systems Utilizing Advanced
Cementitious Composites
This system is a partially cast-in-place high-performance composite frame system
(HPCFS) developed by selectively using high-performance materials, including (1)
continuous fiber-mat high performance fiber reinforced concrete (HPFRCs) called
slurry infiltrated mat concrete (SIMCON), (2) discontinuous fiber HPFRCs called
slurry infiltrated fiber concrete (SIFCON), and (3) high-strength, lightweight aggregate
fiber reinforced concrete (HS-LWA FRC). These advanced composites exhibit superior
strength, energy-absorption capacity, and/or decreased weight, and are thus ideally
suited for an innovative seismic-resistant design. No conventional concrete materials
are used.

2.1 Technical Approach
Partially cast-in-place HPCFSs are built using stay-in-place formwork elements made
by encasing light steel sections and tubes into advanced cementitious composites
including (1) continuous HPFRCs and (2) discontinuous fiber HPFRCs. The "core" of
the beam and column members is cast-in-place HS-LWS FRC. The stay-in-place
formwork also serves as surface reinforcement, thus replacing conventional steel
reinforcement and simplifying casting of the member core by eliminating
reinforcement congestion. Furthermore, by encasing steel elements into HPFRC, their
fire resistance and durability is improved. The construction procedure consists of first
welding or bolting together of the stay-in-place formwork, followed by casting in place
of HS-LWA FRC in both(1) the member core and (2) the beam-column joint region.
Since the subsequent floor can be erected as soon as the steel elements are bolted
together, it is anticipated that the speed of construction per story can be comparable to
that of conventional, prefabricated steel frames. If successful, the proposed concept will
result in advanced concrete frame systems exhibiting high strength and seismic
resistance, while being faster and more cost effective to construct than conventional
cast-in-place systems.

2.3 Slurry Infiltrated Fibrous Concrete (SIFCON)
SIFCON is a high-strength, high-performance material containing a relatively high
volume percentage of steel fibres as compared to SFRC. It is also sometimes termed as

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‘high-volume fibrous concrete’. The origin of SIFCON dates to 1979, when Prof. Lankard
carried out extensive experiments in his laboratory in Columbus, Ohio, USA and proved
that, if the percentage of steel fibres in a cement matrix could be increased substantially,
then a material of very high strength could be obtained, which he christened as SIFCON.

While in conventional SFRC, the steel fibre content usually varies from 1 to 3 percent by
volume, it varies from 4 to 20 percent in SIFCON depending on the geometry of the
fibres and the type of application. The process of making SIFCON is also different,
because of its high steel fibre content. While in SFRC, the steel fibres are mixed
intimately with the wet or dry mix of concrete, prior to the mix being poured into the
forms, SIFCON is made by infiltrating a low-viscosity cement slurry into a bed of steel
fibres ‘pre-packed’ in forms/moulds

The matrix in SIFCON has no coarse aggregates, but a high cementitious content.
However, it may contain fine or coarse sand and additives such as fly ash, micro silica
and latex emulsions. The matrix fineness must be designed so as to properly penetrate
(infiltrate) the fibre network placed in the moulds, since otherwise, large pores may form
leading to a substantial reduction in properties.

A controlled quantity of high-range water-reducing admixture (super plasticizer)may be
used for improving the flowing characteristics of SIFCON. All types of steel fibres,
namely, straight, hooked, or crimped can be used.

Proportions of cement and sand generally used for making SIFCON are 1: 1, 1:1.5, or 1:2.
Cement slurry alone can also be used for some applications. Generally, fly ash or silica
fume equal to 10 to 15% by weight of cement is used in the mix. The water-cement ratio
varies between 0.3 and 0.4, while the percentage of the super plasticizer varies from 2 to
5% by weight of cement. The percentage of fibres by volume can be any where from 4 to
20%, even though the current practical range ranges only from 4 to 12%.

2.4 Slurry Infiltrated Mat Concrete (SIMCON)
SIMCON can also be considered a pre-placed fibre concrete, similar to SIFCON.
However, in the making of SIMCON, the fibres are placed in a “mat form” rather than as
discrete fibres. The advantage of using steel fibre mats over a large volume of discrete

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fibres is that the mat configuration provides inherent strength and utilizes the fibres
contained in it with very much higher aspect ratios. The fibre volume can, hence, be
substantially less than that required for making of SIFCON, still achieving identical
flexural strength and energy absorbing toughness.

SIMCON is made using a non-woven “steel fibre mats” that are infiltrated with a concrete
slurry. Steel fibres produced directly from molten metal using a chilled wheel concept are
interwoven into a 0.5 to 2 inches thick mat. This mat is then rolled and coiled into weights
and sizes convenient to a customer’s application (normally up to 120 cm wide and
weighing around 200 kg).

As in conventional SFRC, factors such as aspect ratio and fibre volume have a direct
influence on the performance of SIMCON. Higher aspect ratios are desirable to obtain
increased flexural strength. Generally, because of the use of mats, SIMCON the aspect
ratios of fibres contained in it could well exceed 500. Since the mat is already in a
preformed shape, handling problems are significantly minimised resulting in savings in
labour cost. Besides this, “balling” of fibres does not become a factor at all in the
production of SIMCON.

Indian Scenerio
In India, SIFCON, CRC, SIMCON and RPC are yet to be used in any major construction
projects. For that matter, even the well-proven SFRC has not found many applications
yet, in spite of the fact that its vast potentials for civil engineering uses are quite well
known. The reason for these materials not finding favour with designers as well as user
agencies in the country could be attributed to the non-availability of steel fibres on a
commercial scale till a few years ago. The situation has now changed. Plain round or flat
and corrugated steel fibres are presently available in the country in different lengths and
diameters. It is, therefore, possible now to use new-age construction materials like
SIFCON and CRC in our country in the construction of several structures that demand
high standards of strength coupled with superior performance and durability.

3. Carbon Fiber Based Linear Reinforcing Elements
Due to their light weight (about one fifth that of steel), high tensile strength (higher
than steel) and good overall environmental durability, carbon fiber based tendons and

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cables are increasingly being used for reinforcement of concrete structures in Japan.
The reduction in weight facilitates better handling and easier field installation
compared to steel. These elements also cause significantly less sag under their own
weight, which increases load capacity while enabling the construction of longer bridge
spans.

Leadline Rods/Tendons
Leadline reinforcing elements are circular rods that are pultruded using unidirectional
carbon fibers at 65% fiber volume fraction with an epoxy resin. The rods have a
specific gravity of 1.6, a relaxation ratio of 2-4% at 20°C, and a coefficient of thermal
expansion of 0.68 x 10
-6
/°C in the longitudinal direction. The rods have a tensile
modulus of 147 GPa and 1.5 to 1.7% elongations at break. Rods are available in a
number of diameters with four major surface types.
Table: Characteristics of Leadline Rods
Round Rods Indented Rods
Designation

R1 R3 R5 R8 R10 R12 R17 D5 D8 D10 D12
Diameter
(mm)
1 3 5 8 10 12 17 5 8 10 12
Tension
(kN)
1.8

16 44 111 170 255 512 40 104 162 245
C/S Area
(mm
2
)
0.8

7.1

19.6

49.0

75.4

113.1

227 17.8

46.1

71.8

108.6

Weight
(g/m)
1.2

11 32 78 119 178 360 30 77 118 177

4. High-Performance Fiber-Reinforced Concrete (HPFRC)

4.1 Introduction
High-Performance Fiber-Reinforced Concrete (HPFRC), a series of new generation
concrete, results from the addition of either short discrete fibers or continuous long
fibers to the cement based matrix. Due to the superior performance characteristics of
this category of SFRC or HPC, its use by the construction industry has significantly
increased in the last 5 years. A very good guide to various Portland cement-based

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composites as well as their constituent materials is available in a recently published
book [Balaguru and Shah 1992].

For highway pavement applications, concretes with early strength are attractive for
potential use in repair and rehabilitation with a view towards early opening of traffic. In
this direction lot of work has been done on high early strength fiber reinforced concrete
(HESFRC) and is being used in practice. Technical papers and reports provide an
extensive database and a summary of comprehensive experimental investigation on the
fresh and mechanical properties of HESFRC. The control high early strength (HES)
concrete (used with the fiber addition) were defined as achieving a target minimum
compressive strength of 35 MPa in 24 hours, as measured from 100 x 200 mm
cylinders.

4.2 Continuous Fiber-Reinforced Concrete
In the last 5 years, there has been significant interest and development in the use of
continuous fiber reinforcement for improving the behavior of cementitious composites
and/or concrete. Fiber Reinforced Polymers (FRP) or sometime also referred to Fiber
Reinforced Plastic are increasingly being accepted as an alternative for uncoated and
epoxy-coated steel reinforcement for prestressed and non-prestressed concrete
applications.
In 1990, the American Concrete Institute formed the ACI Committee 440 on Non-
Metallic Reinforcement. The Committee has just developed a state-of-the-art report on
Fiber Reinforced Plastic (FRP) for Concrete Structures [ACI Committee 440 1996].

4.2.1 Reinforcing Fibers
The principal fibers in common commercial use for civil engineering applications
include glass, carbon and aramid. The most common form of fiber-reinforced
composites used in structural applications is called a laminate. Laminates are made by
stacking a number of thin layers (laminae) or fibers and matrix and consolidating them
into the desired thickness. Fiber orientation in each layer as well as the stacking
sequence of the various layers can be controlled to generate a wide range of physical
and mechanical properties for the composite laminate.
A composite can be any combination of two or more materials as long as the material
properties are different and there is a recognizable region for each material. The

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materials are intermingled. There is an interface between the materials, and often an
inter phase region such as the surface treatment used on fibers to improve matrix
adhesion and other performance parameters via the coupling agent.
Glass has been the predominant fiber for many civil engineering applications because
of an economical balance of cost and specific strength properties. Glass fibers are
commercially available in "E-Glass" formulation (for "Electrical" grade), the most
widely used general-purpose form of composite reinforcement, high strength S-2 glass
and ECR Glass, a modified E-Glass which offers greater alkali resistance. Although
considerably more expensive than glass, other fibers including carbon and aramid are
used for their strength or modulus properties or in special situations as hybrids with
glass.

4.3 Field Applications
Composite materials have been used in a variety of civil engineering applications with
both reinforced and prestressed concrete. They are manufactured as reinforcing
elements, as prestressing and post-tensioning tendons and rods, and as strengthening
materials for rehabilitation of existing structures. Several new structures utilizing FRP
reinforcement are currently underway in USA and Japan.

4.4 applications of high performance SFRC
Pavements
During the past decade, there has been an increasing interest in using high performance
concrete for highway pavements. The main reason for this heightened interest is the
potential economic benefit that can be derived from the early strength gain of high
performance concrete, its improved freeze-thaw durability, reduced permeability, and
increased wear and impact resistance.

Pavement Repairs for Early Opening to Traffic
"Fast Track" Concrete
"Fast track" concrete is designed to give high strength at a very early age without using
special materials or techniques, and it is durable. The early strength is controlled by the
water-cement ratio, cement content and characteristics. Typically, a rich, low-water-
content mix containing 1 to 2 percent calcium chloride will produce adequate strength
and abrasion resistance for opening to traffic in 4-5 hours at temperatures above 10 C.

22
Fast track concrete paving (FTCP) was developed originally by the concrete paving
industry in Iowa. It was pointed out that the benefits of applying FTCP technology in
such applications are (1) a reduced contract period, thus reducing the contract overhead
cost, (2) early opening of the pavement to traffic, (3) minimizing the use of expensive
concrete paving plant and traffic management systems, and (4) reduced traffic delay
costs.

High Strength Concrete Pavement and Bridges
The benefits of using high strength concrete for bridges are well known to bridge
engineers. Over the past several years, there have been a series of design studies
published in the literature, all leading to the same conclusion that the use of high
strength concrete would enable the standard prestressed concrete girders to span longer
distances or to carry heavier loads

4.5 recent activities of organized programs on HPC
4.5.1 Reactive powder Concrete
The need
The upper limit of compressive strength for materials that can be used in commercial
applications continues to be pushed higher and higher. Within the past three years
Portland cement based materials have been developed which have compressive
strengths greater than 200 MPa (2 to 4 times greater than High Performance Concrete).
These materials allow remarkable flexural strength and extremely high ductility, more
than 250 times greater than that of conventional concrete.

The Technology
Reactive Powder Concrete is an ultra high-strength and high ductility composite
material with advanced mechanical properties. Developed in the 1990s by Bouygues'
laboratory in France, it consists of a special concrete where its microstructure is
optimized by precise gradation of all particles in the mix to yield maximum density. It
uses extensively the pozzolanic properties of highly refined silica fume and
optimization of the Portland cement chemistry to produce the highest strength hydrates.

RPC represents a new class of Portland cement-based material with compressive
strengths in excess of 200 MPa range. By introducing fine steel fibers, RPC can

23
achieve remarkable flexural strength up to 50 MPa. The material exhibits high ductility
with typical values for energy absorption approaching those reserved for metals.

The benefits
• RPC is a better alternative to High Performance Concrete and has the potential to
structurally compete with steel.
• Its superior strength combined with higher shear capacity results in significant
dead load reduction and limitless structural member shape.
• With its ductile tension failure mechanism, RPC can be used to resist all but
direct primary tensile stresses. This eliminates the need for supplemental shear and
other auxiliary reinforcing steel.
• RPC provides improve seismic performance by reducing inertia loads with
lighter members, allowing larger deflections with reduced cross sections, and providing
higher energy absorption.
• Its low and non-interconnected porosity diminishes mass transfer making
penetration of liquid/gas or radioactive elements nearly non-existent. Cesium diffusion
is non-existent and Tritium diffusion is 45 times lower than conventional containment
materials.

4.5.2 Compact Reinforced Concrete
CRC is a new type of composite material. In its cement-based version, CRC is built up of
a very strong and brittle cementitious matrix, toughened with a high concentration of fine
steel fibres and an equally large concentration of conventional steel reinforcing bars
continuously and uniformly placed across the entire cross section.

CRC was initially developed and tested by Prof.Bache at the laboratories of Aalborg
Portland cement factory in Denmark. The pioneering experiments carried out at this
laboratory established the vast potential of CRC for applications that warrant high
strength, ductility and durability.

CRC has structural similarities with reinforced concrete in the sense that it also
incorporates main steel bars, but the main bars in CRC are large in number and are
uniformly reinforced. Owing to this and also because of the large percentage of fibres

24
used in its making, it exhibits mechanical behavior more like that of structural steel,
having almost the same strength and extremely high ductility.

CRC specimens are produced using 10-20% volume of main reinforcement (in the form
of steel bars of diameter from about 5 mm to perhaps 40 or 50 mm) evenly distributed
across the cross section) and 5-10% by volume of fine steel fibres. The water-cement ratio
is generally very low, about 0.18% and the particle size of sand in the cement slurry is
between 2 and 4mm.The flow characteristics while mixing and pouring is aided by the
use of micro silica and a dispersant. High-frequency vibration is often resorted to for
getting a the mix compacted and to obtain homogeneity. Prolonged processing time for
mixing, about 15-20 minutes, ensures effective particle wetting and high degree of micro-
homogeneity.

Such highly fibre-reinforced concrete typically has compressive strengths ranging from
150 to 270 MPa, and fracture energy from 5,000 to as much as 30,000 N/m.

CRC beams exhibit load capacities almost equivalent to those of structural steel and
remain substantially uncracked right up to the yield limit of the main reinforcement
(about 3 mm/m), where as conventional reinforced concrete typically cracks at about 0.1-
0.2 mm/m.

It is very strong concrete or composite. It consists of very strong cementitious matrix,
high fraction of steel fiber and high percentage of continuous steel bars. Main
reinforcement is in the form of long bars of 5mm to 40 mm diameter, 10 to 20 percent
are used. Very fine steel fibers are also used to an extent of 5-=10%. Some of the
properties are tabulated below.

Applications
• Large plates and shells designed for very large local loads from shocks and
explosives, large pressure tanks
• High strength to density ratio-used where weight and inertia are important as in
ships and vehicles
• To support large machinery parts

25
• Used in Hybrid structures-High performance structural joints in steel-concrete
structures
• Used as an alternative to steel where corrosion and fire are the main criterion.

26

Properties CRC RCC
Load capacity up to 2mm to 3mm per
m
0.1 to 0.2 mm
per m
Ultimate flexural strength, MPa 140-260 5-25
Ultimate shear
strength, MPa
100-150 with shear
steel
15-20 without
shear steel
3-20
0.25 to 3
Ultimate tensile strength, MPa 100-200 2-12
Ultimate compressive strength,
MPa
150-400 20-80
Young’s Modulus, GPa 30-100 20-40
Density Kg/m
3
3000-4000

2400-2500
Toughness Several times
Fatigue-At 65% Max. load 5 million
compressive stress
cycles
Few
hundreds of
cycles
Fracture energy, N/m 5000- 30,000 100-1000

5. Conclusions

Following conclusions are drawn based on the published literature on SFRC and new
generation high performance fiber reinforced concrete:

1. The growth of the amount of research and applications of steel fiber reinforced
concrete (SFRC) and high performance concrete has been phenomenal in the past
seven or eight years. High performance concrete has become widely accepted
practically on all continents.

2. A generalized definition of high performance concrete seems to have been accepted
by the engineering community. Such a definition is based on achievement of certain
performance requirements or characteristics of concrete for a given application that

27
otherwise can not be obtained from normal concrete as a commodity product. In
many applications use of fiber is mandatory

3. Much of the application of HP-SFRC remains in the areas of long-span bridges and
high-rise buildings. It is used more for bridges than buildings in Europe and Japan,
while more buildings than bridges used HPC in the U. S. However, the situation is
changing. Use of HPC in buildings is increasing these days.

4. Increasing emphasis is being placed on concrete durability than its strength. In
many applications, high strength concrete is used only because of its high durability
quality rather than the need for its strength.

5. Much research continues to be focused on the mechanical properties of high- and
very-high-strength concretes with and without fibers and their structural
applications. The results of this research are being incorporated into various
national codes of practice. However, more information is needed on the behavior of
the concrete at its early age and its relationship to the long-term performance.

6. The Slurry Infiltrated Mat Concrete (SIMCON) and the delivery system for non-
metallic fibers developed are two significant recent developments in the area of
high performance fiber reinforced concrete.

7. There has been significant interest and development in the use of continuous fiber
reinforcement for improving the behavior of concrete. Fiber Reinforced Polymers
(FRP) or sometime also referred to as Fiber Reinforced Plastic are increasingly
being accepted as an alternative for uncoated and epoxy-coated steel reinforcement
for prestressed and non-prestressed concrete applications.

8. Compact Reinforced Concrete and Reactive Powder Concrete (Ductal) have gained
popularity in western countries.

9. Finally the use of this high performance new generation fiber concretes in India is
only in laboratories and in research centers. It will take many years to see in
practice.

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6. References
1. ACI Committee 440. 1996. State-of-the-Art Report on Fiber Reinforced Plastic
(FRP) for Concrete Structures (ACI 440R). ACI Manual of Concrete Practice,
Part 5, American Concrete Institute, Detroit, MI, 68 pp.
2. ACI Committee 544. 1982. State-of-the-Art Report on Fiber Reinforced Concrete
(ACI 544.1R-82). Concrete International, May, Vol. 4, No. 5, pp. 9-30.
3. ACI Committee 544. 1988. Design Considerations for Steel Fiber Reinforced
Concrete (ACI 544.4R-88). Manual of Concrete Practice, Part 5, American
Concrete Institute, Detroit, MI, 18 pp.
4. ACI Committee 544. 1990. State-of-the-Art Report on Fiber Reinforced Concrete.
ACI Manual of Concrete Practice, Part 5, American Concrete Institute, Detroit,
MI, 22 pp.
5. ACI Committee 544. 1993. Guide for Specifying, Proportioning, Mixing, Placing,
and Finishing Steel Fiber Reinforced Concrete. ACI Materials Journal, Jan-Feb,
Vol. 90, No. 1, pp. 94-101. Characteristics. ACI Materials Journal, May-Jun, Vol.
85, No. 3, pp. 189-196.
6. P. N. Balaguru and S. P. Shah. 1992. Fiber Reinforced Cement Composites.
McGraw-Hill, New York, 1992.
7. Nataraja, M. C., Dhang, N and Gupta, A. P (1999)., ‘Statistical Variations in Impact
Resistance of Steel Fiber Reinforced Concrete Subjected to Drop Weight Test’,
Cement and Concrete Research, Pergoman press, USA, Vol. 29, No. 7, 1999, pp.
989-995.
8. Nataraja, M. C., Dhang, N and Gupta, A. P (1999). ‘Stress-strain Curves for Steel
Fiber Reinforced Concrete in Compression’, Cement and Concrete Composites,
UK, Vol. 21, No. 5/6, 1999, pp. 383-390.
9. Nataraja, M. C., Dhang, N and Gupta, A. P (2000)., ‘Toughness Characterisation of
Steel Fiber Reinforced Concrete by JSCE Approach’, Cement and Concrete
Research, Pergoman press, USA, Vol. 30, No. 4, 2000, pp. 593-597.
10. Nataraja, M. C., Dhang, N and Gupta, A. P (2000)., ‘A Study on the Behaviour of
Steel Fiber Reinforced Subjected to Splitting Test’, Asian Journal of Civil
Engineering, Teheran, Iran, Vol. 1, No. 1, Jan. 2000, pp. 1-11.

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11. Nataraja, M. C., Dhang, N and Gupta, A. P (2001). ‘Splitting Tensile Strength of Steel
Fiber Reinforced Concrete’, Indian Concrete Journal, Vol. 75, No. 4, April 2001,
pp. 287-290.
12. Nataraja, M. C., Dhang, N and Gupta, A. P (1998), ‘A Study on Steel Fiber
Reinforced Concrete Composite Using Pulse Velocity Technique’, Indian Concrete
Institute Bulletin, No. 65, Oct.-Dec. 98, pp. 25-27.
13. Nataraja, M. C., Dhang, N and Gupta, A. P (1998), ‘Steel Fiber Reinforced Concrete
under Compression’, The Indian Concrete Journal, Vol. 72, No. 7, July 1998, pp.
353-356.